This invention relates to a novel recording material. More particularly, the invention relates to an information recording material suitable for use in heat mode recording.
Information storage systems in which information is stored by selective ablation, evaporation, removal or modification of a recording medium irradiated spot-wise with a focused beam of laser or the like having high density or strong energy are known as the so-called heat mode recording process to those skilled in the art. The heat mode recording process is a dry process which does not need chemicals or treating solutions and in which a real-time recording can be made. According to this process, information can be quickly recorded in the form of a high contrast image with a large capacity, i.e., the amount of information recordable per unit area of recording medium, and additional information can be recorded later. Due to such advantages, the heat mode recording process is of wide application in the field where a microimage recording medium, a computer-output microfilm, a video disk, a computer signal memory medium or the like is involved.
As materials usable for heat mode recording, there have heretofore been proposed inorganic substances such as metals and organic substances such as dyes or plastics. It is generally known that a thin film made of an inorganic substance is generally better in sensitivity for recording.
The characteristics required of a heat mode recording medium are not only high sensitivity but also a high signal-to-noise ratio, storage stability, archivability, low toxicity and the like. However, there has not yet been proposed such a recording material comprising a thin film of an inorganic substance as will meet these requirements. Recording materials using a chalcogen compound containing sulfur, selenium, tellurium or the like are satisfactory in sensitivity and a signal-to-noise ratio (hereinafter referred to as "S/N ratio") from the standard viewpoint, but involve problems as regards storage stability, achivability and toxicity. On the other hand, recording materials using bismuth, tin or the like do not present problems as regards sensitivity and toxicity but involve problems as regards an S/N ratio storage stability and archivabilty.
Further, we have previously proposed a recording material which comprises a substrate, a multi-layered metallic recording layer formed by depositing in any order bismuth, tin, lead and the like and two stabilizing layers each formed of a metal oxide such as GeO.sub.2, PbO, TiO.sub.2 and/or the like, the multi-layered metallic recording layer being interposed between the stabilizing layers (see Japanese Patent Application Laid-Open Specification No. 54-66147). The proposed recording material is excellent in sensitivity, but has such disadvantages that, when the recording material is selectively irradiated by a laser beam, there are formed holes having, at their respective profiles, irregularities or disorders, causing the S/N ratio to be lowered and the recording material of this kind is poor in storage stability as well as archivability at high temperatures and under high humidities, leading to fatal defects in some applications of the recording material. The term "hole" used herein is intended to mean ablated portions in which information is permanently stored by selective ablation of the recording material by means of an intensity modulated laser beam or the like.
With a view to eliminating the drawbacks accompanying the conventional heat mode recording materials and developing a new heat mode recording material which not only has a high sensitivity and a low toxicity, but also is excellent in S/N ratio, storage stability and archivability, the present inventors have made extensive and intensive researches. As a result, it has been found that when, in a recording material which comprises a substrate, a first stabilizing layer on said substrate, a low toxicity metallic recording layer on a surface of said first stabilizing layer opposite said substrate and a second stabilizing layer on a surface of said metallic recording layer opposite said first stabilizing layer, the first stabilizing layer between the substrate and the low toxicity metallic recording layer is composed of an auxiliary metal oxide layer as an upper layer and an inorganic compound layer as a lower layer for converting said auxiliary metal oxide layer to a surface-flat glassy material, that is, flat glassy material exhibiting no anisotropy in surface tension, the recording material can form, upon exposure to, e.g., a laser beam, excellent holes free of irregularities in shape or profile of hole. The present invention has been made based on such a novel finding.
Accordingly, it is an object of the present invention to provide a recording material which is excellent in sensitivity and storage stability as well as archivability.
It is another object of the present invention to provide a recording material of the above kind, which has a low toxicity.
It is a further object of the present invention to provide a recording material of the character described above, which is excellent in S/N ratio and, accordingly, in shape or profile of hole, that is free of irregularities.